foods Article Mineral Composition and Antioxidant Potential of Coffee Beverages Depending on the Brewing Method Katarzyna Janda 1,* , Karolina Jakubczyk 1 , Irena Baranowska-Bosiacka 2 , Patrycja Kapczuk 2 , Joanna Kochman 1, Ewa R˛ebacz-Maron 3 and Izabela Gutowska 4 1 Pomeranian Medical University in Szczecin, Department of Human Nutrition and Metabolomics, 24 Broniewskiego Street, 71-460 Szczecin, Poland; [email protected] (K.J.); [email protected] (J.K.) 2 Department of Biochemistry, Pomeranian Medical University in Szczecin, 71 Powsta´nców Wlkp. Street, 70-111 Szczecin, Poland; [email protected] (I.B.-B.); [email protected] (P.K.) 3 Department of Vertebrate Zoology and Anthropology, Institute of Biology, University of Szczecin, 13 W ˛askaStreet, 71-415 Szczecin, Poland; [email protected] 4 Department of Medical Chemistry, Pomeranian Medical University in Szczecin, 71 Powsta´nców Wlkp. Street, 70-111 Szczecin, Poland; [email protected] * Correspondence: [email protected] Received: 17 December 2019; Accepted: 21 January 2020; Published: 23 January 2020 Abstract: Coffee, being one of the world’s most popular beverages, is a rich source of dietary antioxidants. The aim of this study was to determine the mineral content and antioxidant activity as well as acidity of coffee beverages depending on the brewing technique. We tested coffee brews made and served at a popular urban coffee shop (Szczecin, Poland). Five coffee brewing techniques were used: Aeropress, drip, espresso machine, French press, and simple infusion. Our findings showed that the brewing method had a significant effect on all parameters tested in the study. The antioxidant activity of the beverages was high (31%–42% inhibition of DPPH (2,2-diphenyl-1-picrylhydrazyl); reduction potential from 3435.06 mol Fe3+/mL to 4298.19 mol Fe3+/mL). Polyphenolic content ranged from 133.90 g (French press) to 191.29 g of gallic acid/L (Aeropress brew), depending on the coffee extraction method. Mineral content was also found to differ between brewing methods. Coffees prepared by simple infusion and Aeropress provided a valuable source of magnesium, manganese, chromium, cobalt, and potassium, whereas the drip brew was found to be a good source of silicon. Keywords: beverages; brewing method; antioxidant potential; total polyphenols content; mineral composition 1. Introduction Along with changes in modern society, as people’s lives are getting faster and more intense, stimulant beverages are becoming increasingly popular. These products have been found to diminish fatigue, enhance concentration, boost productivity, and generally improve performance [1]. Coffee is one of such substances and, in parallel, is one of the most popular beverages [2]. For many people, coffee drinking is part of their lifestyle and a daily habit. Every day, millions of people—about 40% of the world population—begin their day with a morning cup of coffee [3]. Coffee beverages are consumed for various reasons, including their stimulatory effects resulting from the presence of caffeine, health benefits attributed to their rich phytochemistry, and, predominantly, due to excellent taste and aroma. Although flavor, aroma, and the content of caffeine (1,3,7-trimethylpurine-2,6-dione) play a role in its popularity, coffee (both beans and beverages) is a complex chemical mixture, reported to contain more than a thousand of different chemical compounds, including carbohydrates, lipids, nitrogen, vitamins, Foods 2020, 9, 121; doi:10.3390/foods9020121 www.mdpi.com/journal/foods Foods 2020, 9, 121 2 of 16 minerals, alkaloids, and phenolic compounds [2–4]. Various studies have suggested that coffee consumption helps to reduce the risk of number of health conditions, including Alzheimer’s disease, Parkinson’s disease, heart disease, type 2 diabetes mellitus, liver cirrhosis, as well as certain types of disorders [3,4]. Regular consumption of coffee, both green and roasted, is recommended in order to lower the risk of metabolic syndrome [5]. These health-promoting properties of coffee have been linked with its antioxidant content. Indeed, coffee is one of the richest sources of these compounds [4]. Coffee beverages are also a dietary sources of minerals [2,4,6]. The concentrations of minerals and biologically active substances depend of the place of origin of the beans, the degree/intensity of roasting, as well as the brewing method [5–10]. There are no reports in the literature linking the brewing method to the antioxidant and mineral content. In this study, an attempt was made to determine the correlation between the antioxidant activity and the content of minerals in coffee brews. 2. Materials and Methods In this study, we tested coffee brews (espresso blend—100% arabica) made and served at a popular urban coffee shop (an outlet in Szczecin, Poland). 2.1. Coffee Brewing Methods Filtered water was used to make coffee beverages. Aeropress: The Aeropress coffee maker was used. For 250.0 mL of the infusion, 18.0 g of quite coarsely ground coffee was used. The water had a temperature of 93 ◦C, and the pressure was 2–4 bars. The brewing lasted 2 min. Drip: A drip coffee maker device was used. Medium ground coffee beans (18.0 g) were placed in a paper filter. A total of 300.0 mL of water at 92 ◦C was added to the tank and the machine was turned on. After 2.5 min, when the coffee was ready, samples were taken for measurement. Espresso: An espresso machine was used. For 250 mL of the brew, 17.0 g of the most finely ground coffee was used. The water had a temperature of 92 ◦C. The coffee machine was set to 9 bars with regards to pressure. Simple infusion: A total of 17.0 g of very finely ground coffee was placed inside the beaker, 250 mL of hot water (92 ◦C) poured inside, and it was left to steep. After 5 min, coffee samples were taken for analysis. French press: A French press device, also called a press pot or a coffee plunger, was used. The pot was placed on a flat surface, with the plunger pulled out, and 17.0 g of medium ground coffee was added and then 300.0 mL of hot water (92 ◦C) was gently poured inside. Then the plunger was reinserted into the pot on the surface of the beverage and plunged down after 5 min. Under these conditions, a pressure of 1–2 bars was reached. Once the press plunger was pushed down, coffee samples were taken for analysis. 2.2. Spectrophotometric Assay Determination of antioxidant activity, the reduction potential, and polyphenol content were determined using spectrophotometer Agilent 8453UV. All assays were performed in triplicate. For analysis, infusions were diluted 20 times. 2.2.1. Determination of Antioxidant Activity The antioxidant activity of samples was measured with spectrophotometric method using synthetic radical DPPH (2,2-diphenyl-1-picrylhydrazyl, Sigma Aldrich, Darmstadt, Germany). Antioxidant potential (antioxidant activity, inhibition) of tested solutions has been expressed by the percent of DPPH inhibition [6]. Foods 2020, 9, 121 3 of 16 2.2.2. Determination of Total Polyphenol Content Determination of polyphenols was performed according ISO (International Organization for Standarization) 14502-1 using Folin–Ciocalteu reagent [11]. A total of 5.0 mL of a 10% Folin–Ciocalteau solution and 1.0 mL of test sample were successively introduced into the vial. The sample was shaken vigorously, and after 5 min, 4.0 mL of 7.5% Na2CO3 solution was added. The prepared solution was incubated for 60 min at room temperature. Reference solution was prepared the same way, but distilled water was added instead of the tested sample. Absorbance at 765 nm was measured. Total polyphenols content (ppm) was determined from the calibration curve using gallic acid as the reference standard. 2.2.3. Determination of the Reduction Potential by the FRAP (Ferric Reducing of Antioxidant Power) Method The FRAP method, used to determine the total reduction potential, is based on the ability of the test sample to reduce Fe3+ ions to Fe2+ ions. The FRAP unit determines the ability to reduce 1 mole Fe3+ to Fe2+ [12]. Absorbance at 593 nm was measured. 2.3. Determination of Total Acidity by Titration The total acidity of coffee beverages subjected to analysis was determined by titrating the sample with a standard solution of NaOH in the presence of phenolphthalein until the color changed to light pink and stayed pink for at least 30 s [13]. The result was reported in grams per 100 mL of the infusion and expressed in units of malic acid. 2.4. Determination of Mineral Content Samples (coffee beans: n = 3; coffee beverages: n = 3 of each type of coffee drink) were analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES, ICAP 7400 Duo, Thermo Scientific (Waltham, MA, USA) equipped with a concentric nebulizer and cyclonic spray chamber to determine their Ca, Fe, Mg, K, Na, Sr, Zn, and P content. Analysis was performed in radial and axial mode. The samples were mineralized using microwave digestion system MARS 5 (CEM, Matthews, NC, USA). The weight of solid samples given to analysis was at least 0.1 g. The volume of liquid samples was 0.75 mL. The samples were transferred to clean polypropylene tubes. Then, 4 mL of 65% HNO3 (Suprapur, Merck, Darmstadt, Germany) was added to each vial and each sample was allowed 30 min pre reaction time in the clean hood. After completion of the pre-reaction time, 1 mL of non-stabilized 30% H2O2 solution (Suprapur, Merck, Darmstadt, Germany) was added to each vial. Once the addition of all reagents was complete, the samples were placed in special Teflon vessels and heated in a microwaved digestion system for 35 min at 180 ◦C (15 min ramp to 180 ◦C and maintained at 180 ◦C for 20 min).